Re: [PATCH] TSC scaling for live migration between platforms with different TSC frequecies

[John Levon <levon@movementarian.org>]

On Thu, Jun 18, 2009 at 08:58:49AM -0700, Dan Magenheimer wrote:

> Other apps (and/or the OS kernel) may use TSC to
> approximate the passage of time, and for these apps
> (and gettimeofday in the Linux kernel), this TSC scaling
> patch is a must.  Unfortunately, both kinds of apps could
> be running simultaneously on the same guest.  And
> in either case, RDTSC frequency may be quite high.

Certainly Solaris relies on the TSC for time-keeping, and uses it very
heavily. To the extent that I doubt it's even feasible to migrate to a
machine where scaling needs to be done, and such a migration should be
refused, since it would essentially kill the guest.

> question is:  If it is important to ALWAYS emulate RDTSC,
> can the Xen code be written to handle RDTSC emulation
> much faster?  If it could be made fast enough, the

I'd be amazed if this were possible.

regards
john